Originally Posted by 824TSV
Its a good idea, but probably a dud. I have the iphone app for a heli tach which was a waste of money. Doesn't work properly.
The author of this app here. I have really tried my best to make it work and so far it seems to work pretty well for all that have contacted me (including my testers). It is important to have a correct angle (see description) and fairly good lighting conditions. When I tested with by bevel box I got a difference of 0.1 degrees. (10.3 on bevel box and 10.2 in the app). It will however vary depending on how steady you hold the camera, angle against the rotor head etc. One good thing is that it does not need any calibration as it measures the angles between the blades, so even if you have the heli on a table that is not level etc it will still measure the angles correctly.
Unfortunately one cannot re-fund using AppStore, but if you have an Android you can buy the app and test it before the refund period expires. If you do not like it, you can return the app and get the money back. I guess the refund time is pretty short, but if you plan (i.e. have the heli ready) you should be able to test and evaluate before this happens.